Hubble Space Telescope Planetary Camera Images of NGC 1316

We present HST Planetary Camera V and I~band images of the central region of the peculiar giant elliptical galaxy NGC 1316. The inner profile is well fit by a nonisothermal core model with a core radius of 0.41" +/- 0.02" (34 pc). At an assumed distance of 16.9 Mpc, the deprojected luminosity density reaches \sim 2.0 \times 10^3 L_{\sun} pc$^{-3}$. Outside the inner two or three arcseconds, a constant mass-to-light ratio of $\sim 2.2 \pm 0.2$ is found to fit the observed line width measurements. The line width measurements of the center indicate the existence of either a central dark object of mass 2 \times 10^9 M_{\sun}, an increase in the stellar mass-to-light ratio by at least a factor of two for the inner few arcseconds, or perhaps increasing radial orbit anisotropy towards the center. The mass-to-light ratio run in the center of NGC 1316 resembles that of many other giant ellipticals, some of which are known from other evidence to harbor central massive dark objects (MDO's). We also examine twenty globular clusters associated with NGC 1316 and report their brightnesses, colors, and limits on tidal radii. The brightest cluster has a luminosity of 9.9 \times 10^6 L_{\sun} ($M_V = -12.7$), and the faintest detectable cluster has a luminosity of 2.4 \times 10^5 L_{\sun} ($M_V = -8.6$). The globular clusters are just barely resolved, but their core radii are too small to be measured. The tidal radii in this region appear to be $\le$ 35 pc. Although this galaxy seems to have undergone a substantial merger in the recent past, young globular clusters are not detected.Comment: 21 pages, latex, postscript figures available at ftp://delphi.umd.edu/pub/outgoing/eshaya/fornax

Supermassive Black Holes and the Evolution of Galaxies

Black holes, an extreme consequence of the mathematics of General Relativity, have long been suspected of being the prime movers of quasars, which emit more energy than any other objects in the Universe. Recent evidence indicates that supermassive black holes, which are probably quasar remnants, reside at the centers of most galaxies. As our knowledge of the demographics of these relics of a violent earlier Universe improve, we see tantalizing clues that they participated intimately in the formation of galaxies and have strongly influenced their present-day structure.Comment: 20 pages, - This is a near-duplicate of the paper in Nature 395, A14, 1998 (Oct 1

Selection Bias in Observing the Cosmological Evolution of the Mbh-sigma and Mbh-L Relationships

Programs to observe evolution in the Mbh-sigma or Mbh-L relations typically compare black-hole masses, Mbh, in high-redshift galaxies selected by nuclear activity to Mbh in local galaxies selected by luminosity L, or stellar velocity dispersion sigma. Because AGN luminosity is likely to depend on Mbh, selection effects are different for high-redshift and local samples, potentially producing a false signal of evolution. This bias arises because cosmic scatter in the Mbh-sigma and Mbh-L relations means that the mean log(L) or log(sigma) among galaxies that host a black hole of given Mbh, may be substantially different than the log(L) or log(sigma) obtained from inverting the Mbh-L or Mbh-sigma relations for the same nominal Mbh. The bias is particularly strong at high Mbh, where the luminosity and dispersion functions of galaxies are falling rapidly. The most massive black holes occur more often as rare outliers in galaxies of modest mass than in the even rarer high-mass galaxies, which would otherwise be the sole location of such black holes in the absence of cosmic scatter. Because of this bias, Mbh will typically appear to be too large in the distant sample for a given L or sigma. For the largest black holes and the largest plausible cosmic scatter, the bias can reach a factor of 3 in Mbh for the Mbh-sigma relation and a factor of 9 for the Mbh-L relation. Unfortunately, the actual cosmic scatter is not known well enough to correct for the bias. Measuring evolution of the Mbh and galaxy property relations requires object selection to be precisely defined and exactly the same at all redshifts.Comment: 28 pages, 6 figures, submitted to the Astrophysical Journa

Blazars in the early Universe

We investigate the relative occurrence of radio--loud and radio-quiet quasars in the first billion years of the Universe, powered by black holes heavier than one billion solar masses. We consider the sample of high-redshfit blazars detected in the hard X-ray band in the 3-years all sky survey performed by the Burst Alert Telescope (BAT) onboard the Swift satellite. All the black holes powering these blazars exceed a billion solar mass, with accretion luminosities close to the Eddington limit. For each blazar pointing at us, there must be hundreds of similar sources (having black holes of similar masses) pointing elsewhere. This puts constraints on the density of billion solar masses black holes at high redshift (z>4), and on the relative importance of (jetted) radio-loud vs radio-quiet sources. We compare the expected number of high redshift radio--loud sources with the high luminosity radio-loud quasars detected in the Sloan Digital Sky Survey (SDSS), finding agreement up to z~3, but a serious deficit at z>3 of SDSS radio-loud quasars with respect to the expectations. We suggest that the most likely explanations for this disagreement are: i) the ratio of blazar to misaligned radio-sources decreases by an order of magnitude above z=3, possibly as a result of a decrease of the average bulk Lorentz factor; ii) the SDSS misses a large fraction of radio-loud sources at high redshifts, iii) the SDSS misses both radio-loud and radio-quiet quasars at high redshift, possibly because of obscuration or because of collimation of the optical-UV continuum in systems accreting near Eddington. These explanations imply very different number density of heavy black holes at high redshifts, that we discuss in the framework of the current ideas about the relations of dark matter haloes at high redshifts and the black hole they host.Comment: MNRAS, in pres

Cosmic Background dipole measurements with Planck-High Frequency Instrument

This paper discusses the Cosmic Background (CB) dipoles observations in the framework of the Planck mission. Dipoles observations can be used in three ways: (i) It gives a measurement of the peculiar velocity of our Galaxy which is an important observation in large scale structures formation model. (ii) Measuring the dipole can give unprecedent information on the monopole (that can be in some cases hard to obtain due to large foreground contaminations). (iii) The dipole can be an ideal absolute calibrator, easily detectable in cosmological experiments. Following the last two objectives, the main goal of the work presented here is twofold. First, we study the accuracy of the Planck-HFI calibration using the Cosmic Microwave Background (CMB) dipole measured by COBE as well as the Earth orbital motion dipole. We show that we can reach for HFI, a relative calibration between rings of about 1% and an absolute calibration better than 0.4% for the CMB channels (in the end, the absolute calibration will be limited by the uncertainties on the CMB temperature). We also show that Planck will be able to measure the CMB dipole direction at better than 1.7 arcmin and improve on the amplitude. Second, we investigate the detection of the Cosmic Far-Infrared Background (FIRB) dipole. Measuring this dipole could give a new and independent determination of the FIRB for which a direct determination is quite difficult due to Galactic dust emission contamination. We show that such a detection would require a Galactic dust emission removal at better than 1%, which will be very hard to achieve.Comment: 10 pages, 13 figures, submitted to A&A, uses aa.sty V5.

Cosmic Microwave Background Dipole induced by double inflation

The observed CMBR dipole is generally interpreted as the consequence of the peculiar motion of the Sun with respect to the reference frame of the CMBR. This article proposes an alternative interpretation in which the observed dipole is the result of isocurvature perturbations on scales larger than the present Hubble radius. These perturbations are produced in the simplest model of double inflation, depending on three parameters. The observed dipole and quadrupole can be explained in this model, while severely constraining its parameters.Comment: Latex, 9 pages, no figure, to appear in Phys. Rev.